Ellagitannins are monomeric, oligomeric, and polymeric polyphenols that are abundant in some fruits, berries and nuts, such as pomegranates, raspberries, strawberries, black raspberries, walnuts and almonds. The fruits and berries are widely consumed fresh and as beverages, such as juice, and these have been reported to promote health.
In commercial fruit juice processing methods, ellagitannins, which are particularly abundant in some fruit peels, are extracted in large quantities into the juice. Ellagitannins belong to the chemical class of hydrolyzable tannins, which release ellagic acid upon hydrolysis. In vitro studies have suggested that ellagitannins, at concentrations in the range of 10-100 micromolar (μM), have potential anti-oxidant, anti-atherogenic, anti-thrombotic, anti-inflammatory, and anti-angiogenic effects. Fruits may have different ellagitannins that are predominant, for example, in fruit juice prepared from pomegranate, the predominant ellagitannin is punicalagin [2,3 hexahydroxydiphenoyl-4,6-gallagylglucose], which occurs as a mixture of isomers. The reported potent anti-oxidant properties of pomegranate juice have been attributed to the high content of punicalagin isomers, which can reach levels >2 g/L of juice. Ellagitannins have also been identified as the active anti-atherogenic compounds in pomegranate juice. It has also been suggested that pomegranate ellagitannins and pomegranate fruit extracts inhibit the proliferation of human cancer cells and modulate inflammatory sub-cellular signaling pathways and apoptosis. See, for example, Seeram et al. (2005) J Nutr Biochem. 16:360-7; Adams et al. (2006) J Agric Food Chem. 54:980-85; Afaq et al. (2005) Photochem Photobiol. 81:38-45; Afaq et al. (2005) Int J Cancer. 113:423-33. Pomegranate fruit extract has also been reported to reduce prostate tumor growth and prostate serum antigen (PSA) levels in athymic nude mice implanted with CWR22Rv1 prostate cells. Malik et al. (2005) Proc Natl Acad Sci. 102:14813-8.
Unfortunately, for the most part ellagitannins are poorly absorbed by the human gut. However, a number of metabolites derived from ellagitannins are absorbed by the human gut, including certain metabolites ultimately formed in the gut by commensal microorganisms (i.e., intestinal microflora).
Ellagitannins release ellagic acid under physiological conditions in vivo, and ellagic acid is then gradually metabolized by the gut microflora in the intestine to produce urolithin D, urolithin C, urolithin A (UA) and urolithin B (UB). Once the metabolites are absorbed, they undergo glucuronidation and once in the liver, they are further metabolized to produce glucuronides, and/or sulfates, to give a combination of metabolites secreted in the bile.
Urolithins are metabolites of ellagic acid, punicalagin (PA), punicalin (PB), tellimagrandin (TL), and other ellagitannins (Cerda, Espin et al. 2004; Cerda, Periago et al. 2005). Ellagic acid (EA) is abundant in pomegranate juice (Gil, Tomas-Barberan et al. 2000). The ellagitannin tellimagrandin (TL) has been previously isolated and characterized before from pomegranate and other plants (Tanaka, Nonaka et al. 1986; Tanaka, Nonaka et al. 1986; Satomi, Umemura et al. 1993). Structural formulas for UA, PA, PB, EA, and TL are presented in FIG. 1.
Considerable efforts have been made to understand the mechanism of metabolic disorders, neurodegeneration and cognitive decline, so as to better design treatment modalities including those based on natural products. One of the key observations has been therole of declining mitochondrial energy production, corresponding with increased oxidative stress and apoptosis, plays a significant role in degenerative diseases and the process of aging. A variety of degenerative diseases have now been shown to be caused by mutations in mitochondrial genes encoded by the mitochondrial DNA (mtDNA) or the nuclear DNA (nDNA). Importantly, somatic mtDNA mutations accumulate with age in post-mitotic tissues in association with the age-related decline in mitochondrial function and are thought to be an important factor in aging and senescence. Inherited diseases can result from mtDNA base substitution and rearrangement mutations and can affect the CNS, heart and skeletal muscle, and renal, endocrine and hematological systems.
Mitochondria generate most of the cellular energy by oxidative phosphorylation (OXPHOS), and they produce most of the toxic reactive oxygen species (ROS) as a by-product. Genetic defects that inhibit OXPHOS also cause the redirection of OXPHOS electrons into ROS production, thus increasing oxidative stress. A decline in mitochondrial energy production and an increase in oxidative stress can impinge on the mitochondrial permeability transition pore (mtPTP) to initiate programmed cell death (apoptosis). The interaction of these three factors is believed to play a major role in the pathophysiology of degenerative diseases and the aging process, which affects all tissues of the body.
In the normal brain, optimal cognitive function mainly relies on the activity and communication between neurons, highly complex cells able to convey electric signals and elicit chemical neurotransmission. Neuronal function depends on long and complex cellular processes that can extend over centimeters or even meters to connect neurons or target cells, and can make more than 100,000 synaptic contacts. As such, neurons are highly dependent on energy supply and, therefore, are exposed to oxidative stress damage. Cognitive function is dependent on a careful balance of intracellular signaling that takes place within a complex network of neurons. Optimal cognitive function can be impaired by numerous factors such as aging, cellular stress, chronic stress, and neurodegenerative disorders. Cognitive decline may be characterized by a decrease in performance in thinking, learning, memory, alertness, and/or impaired psychological skills, as well as by depression and anxiety.
Mitochondrial function has also been shown to be important in metabolic disorders. Diabetes and obesity have been correlated with compromises in mitochondrial function. It has been suggested that the coupling efficiency in mitochondria, or the proportion of oxygen consumption necessary to make ATP, is related to levels of obesity, with high coupling efficiency possibly resulting in higher deposition of fat stores (Harper, Green et al. 2008). In diabetes, recent work has suggested that mitochondrial dysfunction is a cause of insulin insensitivity in myocytes and adipocytes, as a result of insufficient energy supply or defects in the insulin signaling pathway (Wang, Wang et al. 2010).